Experimental study of A0 Lamb wave tomography
Corrosion damage in inaccessible regions presents a significant challenge to the petrochemical industry, and determining the remaining wall thickness is important to establish the remaining service life. Guided wave tomography is one solution and involves transmitting Lamb waves through the area of interest and using the received signals to reconstruct the remaining wall thickness. This avoids the need to access all points on the surface, making the technique well suited to inspection beneath supports. For this purpose a tomography system for pipe inspections is developed using low frequency A0 Lamb waves that are excited and detected with two arrays of electromagnetic acoustic transducers (EMATs). Two different defect depths are considered with different contrasts relative to the nominal wall thickness and in a first step, the repeatability of the measurements is demonstrated. Due to the limited view array configuration, the maximum depth of the reconstruction underestimates the true depth. In a second experimental study, the influence of a pipe clamp on the thickness reconstruction is considered, representing an inspection problem with restricted access. Preliminary results have shown that the maximum defect depth is further underestimated when compared to the thickness reconstructions without the clamp. However, it is possible to detect the defect underneath the clamp for all conducted experiments.